Device for damping and scattering hydrosound in a liquid

ABSTRACT

A device is provided for damping hydrosound in liquid emitted from a sound-emitting body in the liquid. The device includes a plurality of envelope bodies distributed in the liquid in an area of the hydrosound-emitting body and at a distance from each other. A material, diameter and pressure of each envelope body is configured such that a natural frequency of the envelope body corresponds to an emitted frequency range of the hydrosound so as to dampen the hydrosound. The device also includes at least one mass body disposed in the liquid. The envelope bodies are connected to the mass bodies so as to prevent the envelope bodies from rising up in the liquid.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 12/936,235, filed Oct. 4, 2010, which is a U.S. National Phaseapplication under 35 U.S.C. §371 of International Application No.PCT/DE2009/000413, filed Apr. 1, 2009, which claims benefit to GermanApplication No. DE 10 2008 017 418.1, filed Apr. 3, 2008.

FIELD

The invention relates to a device for damping and scattering hydrosoundand/or wave motions in a liquid, particularly water, by means of atleast one envelope body enclosing a gas.

BACKGROUND

Sound waves propagate very well in liquids, since liquids such as, forexample, water generally have a low damping capacity. In the sea, soundwaves caused by, for example, whales or underwater construction sitesare carried over many kilometers. Sound waves, however, can be hazardousto the animals in the water, such as marine mammals or fish. Thisapplies particularly to artificially generated sound waves. Pile drivinggives rise to particularly powerful acoustic emissions in water.

In addition to increasing shipping traffic, the erection of offshorewind energy installations is one of the sources of acoustic emissions inwater that will increase in the future and that impose substantialstresses upon animals. Measures to reduce the acoustic emissions and toadhere to allowable limit values are necessary in order that animals, inparticular protected species such as, for example, porpoises and seals,are not adversely affected by technical installations in the sea, inharbor areas and in other bodies of water.

Acoustic insulation and acoustic damping are known for the purpose ofreducing the propagation of sound and wave motions in water.

Acoustic insulation is the use of reflective obstacles to impede thepropagation of sound. The strength of the reflection is dependent on thedifference in the wave resistances of the sound-carrying medium and theimpeding medium. This effect is particularly pronounced in the case ofacoustic transmission from water to air and then back from air to water.The reduction of sound propagation in water using the principle of anacoustic insulating and shielding air layer is known from DE 103 02 219A1. The method, disclosed in the document, for reducing the transmissionof sound and wave motions in the case of an object in the water relatesto realization of the air layer that is to fully surround the objectthrough, for instance, tubes, air cushions, foam layers or porous orair-filled films. In each case, the sound source must be enveloped in acompletely form-fit closed manner in order to achieve the hoped-foracoustic insulating effect. Even small openings, as in the case of adoor gap or similar to structure-borne sound bridges, reduce theacoustic insulating effect considerably and render it ineffective.Depending on the design of the acoustic insulation, the acousticinsulating effect is greatly reduced in the resonant ranges of thedevice.

Acoustic insulation thus requires a complete enveloping of the soundsource. In the establishing of relieved foundation structures or thedriving of sheet piling in water, complete form-fit enveloping isachievable only with a very large amount of resource, but is usually notachievable. Particularly in the offshore domain, with the motion of thesea and great depth of water, the manipulation of acoustic insulationstructures is resource-intensive. Only with difficulty can a completedecoupling, i.e. the placing in the water of a continuous, vertical airlayer that completely surrounds the sound source, be realized with aneconomically justifiable resource expenditure, particularly in the caseof water depths of over ten meters. Reasons for this are the waterpressure that is present and the horizontal forces from the current. Adecoupling, i.e. acoustic insulation, by means of air-filled hollowbodies, such as that described in the publication DE 103 02 219 A1,always has sound bridges and resonant ranges. Thus, the air layer at theconnection points of the individual hollow bodies is extremely thin, oreven discontinuous. Since the resonant frequency of the hollow bodies isoften in the lower frequency ranges of less than 100 Hz, thesefrequencies, typically often generated in the case of drilling andpile-driving operations, are transmitted or even amplified by theoscillating hollow bodies.

Further devices for acoustic insulation are described by Dr. ManfredSchulz-von Glahn, Dr. Klaus Betke and Dr. Georg Nehls in theirpublication “Minderung des Unterwasserschalls bei Rammarbeiten fürOffshore-WEA—Praktische Erprobung verschiedener Verfahren unterOffshore-Bedingungen”. Moreover, a sound scattering and damping method,the so-called bubble curtain, is also mentioned in the publication.

Acoustic damping, by contrast, is the absorption of the sound, i.e. theconversion of the mechanical acoustic energy into heat, whereby theacoustic energy is nullified. The publication U.S. Pat. No. 3,647,022 Adiscloses a device for damping sound waves in a liquid medium, whereinindividual sound damper elements are arranged on a carrier element, awall of a vessel that accommodates the liquid medium constituting thecarrier element that absorbs the resulting sound pressure.

In the case of liquids, which as a medium have a low damping capacity,the sound can also be damped, for example, by the oscillations of amultiplicity of gas bubbles. The sound excitation in the range of thenatural frequency of the individual gas bubble results in a veryeffective reduction of the sound amplitudes, both through scattering andthrough absorption of the sound. The natural frequency of a gas bubblein this case is dependent, inter alia, on the elasticity, the pressureand the diameter of the gas bubble.

Curtains of gas bubbles have already been applied successfully inpile-driving operations in shallow water. In addition to the resonantfrequency, the rise velocity of the gas bubbles is also dependent on thediameter of the gas bubbles. In a curtain having a mixture of gasbubbles of differing diameters, the larger bubbles rise very much morequickly. The gas bubbles that rise up slowly must be shielded fromcurrent influences, by means of appropriate measures. For this, it isusual to employ a so-called guided bubble curtain, in which the curtainof gas bubbles rises up within a body, the body being impermeable tocurrent and thus having to absorb the horizontal forces from the currentacting upon it. A curtain of gas bubbles can be used to influence thehydroacoustic properties of the medium water. For this purpose, the gasbubbles are usually obtained from the ambient air present above thewater level and are produced in the water, usually in a plurality ofplanes, by means of technical equipment such as pumps and lines.

Each gas bubble is released in the water and held together by thesurface tension of the water. The transmission of the sound in this caseis reduced, in essence, through damping, scattering and absorption. Sucha curtain is produced by means of tubes and/or pipelines laid on theground. The tubes and/or pipelines have openings, of a defined size andquantity, through which gas is forced into the surrounding water.Usually, the air present above the water level is used as the gas forthe bubbles. This air is compressed by compressors and conveyed to thetubes and/or pipelines laid on the ground. The production of suchcurtains of bubbles of a defined size and quantity becomes moredemanding as water depth increases, since the volume of the individualrising bubble is dependent on the water depth. As the gas bubble risesin the water, the water pressure surrounding the gas bubble decreases,which results in a considerable change in the size of the gas bubble,and therefore in the effective frequency range, and in uncontrolledconditions due to non-controllable divisions and combinations of the gasbubbles. Since the resonant frequency of the bubble varies with itsvolume, it is necessary for bubbles to be produced continuously atdiffering depths, for example every five meters, in order to achieve, tosome extent, controlled conditions of acoustic damping.

The production of a curtain of bubbles for the purpose of damping soundemissions from industrial installations such as oil drills orpile-driving operations for wind power installations necessitates thecompression and conveyance of large quantities of compressed gas. Theequipment required for this has a high energy requirement and highoperating costs, which increase as water depth increases. Soundemissions are transmitted, not only through the water, but also throughthe ground, and can then be emitted back into the water at a distancefrom the sound source. From an economic and ecological point of view,however, the production of a large-area curtain is questionable. Thecurtain is also adversely affected by the currents in the water,resulting in the bubbles being generated in an uncontrollable mannerand, ultimately, in a less effective acoustic damping.

SUMMARY

An aspect of the invention provides a device by means of which thetransmission and propagation of sound and wave motions in water can bereduced, the device being such that it can be used, in a manner that isas simple, fault-free and controllable as possible, both in motionlesswaters and in strong currents and, irrespective of the water depth, hasa low energy requirement and, insofar as possible, gives rise to nooperating costs, and large-scale application is also possible at lowcost.

In an embodiment, the present invention provides a device for dampinghydrosound in liquid emitted from a sound-emitting body in the liquid.The device includes a plurality of envelope bodies distributed in theliquid in an area of the hydrosound-emitting body and at a distance fromeach other. A material, diameter and pressure of each envelope body isconfigured such that a natural frequency of the envelope bodycorresponds to an emitted frequency range of the hydrosound so as todampen the hydrosound. The device also includes at least one mass bodydisposed in the liquid. The envelope bodies are connected to the massbodies so as to prevent the envelope bodies from rising up in theliquid.

In a particular embodiment, the present invention provides a devicethrough which water can flow, in particular in the direction of soundpropagation, and which has a multiplicity of envelope bodies that are ata distance from one other and are each surrounded by water on all sides.Owing to the individual envelope bodies, and thus also the individualgas volumes or gas bubbles, being at a distance from one another, it hasbecome possible to reduce the transmission and propagation of sound andwave motions in water by means of industrially prefabricated envelopebodies, water currents and animals being able to pass the device withoutexerting large forces upon the device. The invention consists inreplacing the sound-damping effect of a conventional bubble curtain,whose individual air bubbles are held together by the surface tension ofthe water, by a bubble curtain having artificially produced hollowbodies as bubble envelopes. In this case, water flows around theenvelope bodies on all sides. Ideally, the envelope body is composed ofan elastic material and is filled with air. Expediently, the device isset up in such a way that the individual envelope bodies are preventedfrom rising up.

For this purpose, the device comprises a carrier element and a massbody. The envelope bodies in this case are arranged at a distance fromone another on the carrier element. The bubble-type envelope bodies,distributed freely in the water and arranged on a carrier element, areprevented by the mass body from rising up. The envelope bodies, however,are not connected to one another either non-positively or positively orin a space dividing manner.

Surprisingly, the fact that the envelope bodies are at a distance fromone another makes it possible to reduce sound propagations in water,also called hydrosound, and wave motions. In this case, an effectsimilar to the acoustic damping and acoustic scattering by means of abubble curtain is produced. In contrast to the conventional bubblecurtains, the gas enclosed by the envelope body is prevented by the massbody from rising up in the water. The gas volumes are thus maintainedand do not have to be continuously renewed. There is no need for acontinuous compressed air supply, which, particularly in the offshoredomain and in deep water, is demanding of resources. Likewise, theenvironmental conditions prevailing in the water, such as current orwater pressure, exert only a slight influence upon the device, sincewater flows through and/or passes around this device, since theeffective volume concentration of the gas bubbles is in the range ofapproximately a per thousand. The envelope bodies in this case arearranged at a distance radially, axially and in the circumferentialdirection from a body emitting hydrosound. In addition, a gas volumeenclosed in an envelope body has a constant mass, and cannot fuse withanother gas bubble, or divide.

In order that the device does not move to the water surface because ofthe buoyancy force of the gas, it is expedient for the device, throughthe mass body, to have a weight that is equal to and/or greater than thebuoyancy force of the device. The carrier elements to which the envelopebodies are fastened are realized as a multiplicity of individual cables,which are fastened, close to the ground, at least indirectly, forexample by means of a net, to at least one mass body. These carrierelements, which to a very large extent are aligned vertically, owing tothe buoyancy of the envelope bodies, can move freely horizontally, atleast to a limited extent. They do not constitute any obstacle for fishor other marine life, since the carrier elements yield when an animalswims against the carrier element or envelope body of the device.

As in the case of the conventional, natural air bubbles in water,air-filled bubble envelopes, made from a flexible, thin-walled, elasticmaterial, that are distributed in the water constitute dampedresonators. The sound excitation near the natural frequency of theenvelope body results in a very effective reduction of the soundamplitudes, both through scattering and through absorption. Above all,the damping effect is limited to a range around the natural frequency ofthe envelope bodies and to the range above the natural frequency. Thenatural frequency here is a function of the diameter, the adjustableelasticity and the internal pressure of the envelope body.

The diameter of an envelope body that is suitable for acoustic dampingin the case of offshore construction sites, i.e. for a frequency rangefrom 100 Hz to 1000 Hz, lies in a range from millimeters up to a fewcentimeters. For frequencies above 1000 Hz, the suitable diameters ofthe envelope bodies lie in the range of a few millimeters and below.

Through the choice of the material and the diameter, the individualprefabricated envelope bodies can be precisely matched to the requiredfrequency range and distributed accordingly in the water, around thesound-emitting body, since, unlike natural bubbles, their position,particularly their vertical position, in the water, and therefore theireffectiveness does not alter.

Consequently, a substantial advantage is achieved in comparison withnatural bubbles and bubble curtains, since the air-filled envelopebodies according to the invention, which are capable of resonance andhave a high damping capacity, can easily be produced, for example, withdiameters of several centimeters and much greater. In the case ofpile-driving operations in water, in the level determinant lowerfrequency range from approximately 50 Hz to 600 Hz, it is preciselybubbles of such a diameter that very effectively reduce the hydrosoundthrough resonant oscillations. Moreover, bubbles of such magnitude arealso effective above the respective natural frequency up to the kHzrange, and can thus cover the entire relevant frequency range.

Large natural bubbles are unstable, ascend rapidly and disintegrate. Inaddition, owing to the quantity of compressed air required, it isdifficult to produce them economically. Since the use of the air-filledenvelope bodies makes it possible to dispense with a compressed airsupply, and in the lower frequency range they are also capable ofresonance around approximately 100 Hz and are very effective, they canalso be used, advantageously, to reduce substantially the hydrosoundemissions of finished offshore constructions such as, for example, windpower installations in the operating state. The sound energy radiatedunder water generally lies within this frequency range in all operatingstates.

Moreover, the distribution of the bubbles, or envelope bodies, in thewater renders the water body compressible, whereby the reduction of thesound amplitudes is improved, both through a substantially increasedeffective scattering cross-section and through absorption of the sound.

Altogether, the frequency-dependent reduction of a sound wave passingthrough the body of water is a function, substantially, of the naturalfrequencies, the damping capacity, the distribution, the concentrationof the air-filled envelope bodies and the dimension of the devicethrough which the sound wave passes. In the case of the device accordingto the invention, the effective volume concentration is even in therange of a per thousand.

It is advantageous for the device that the envelope bodies can bepositioned vertically in the water and/or horizontally in a flat manneron the ground. Since the sound waves also propagate via the ground andcan emit into the water at a distance from the sound source, it is thuspossible for the sound propagation via the ground also to be reducedwith little resource expenditure. It is equally possible to cover theground with envelope bodies fastened to cables or nets as with cages,distributed on the ground, in which the gas-filled envelope bodies arearranged.

It is particularly advantageous that the envelope body is a flexiblemembrane composed of a thin-walled, elastic material having a highdamping capacity. The flexibility and elasticity of the envelope bodypermit an effective oscillatory excitation of the gas volume, as in thecase of a natural gas bubble. The use of a material having a highdamping capacity increases the overall damping of the resonantlyoscillating gas volume.

It is economical to fill the envelope body with air. On the other hand,there are particular technical advantages in filling the envelope bodywith a gas and/or with a soft, open-pore and/or closed-pore materialhaving a high damping capacity. It is thus possible to improve theacoustic properties of the gas volume or to adjust them according to theintended application.

It is advantageous that the envelope body is composed of an organicand/or inorganic material. It is possible, for example, to constitutethe envelope body from a bubble alga (Ventricaria ventricosa), whichgrows on the carrier element or on the sea bed. Other suitable materialsare latex or animal intestines.

The carrier element can be constituted, for example, by a woven fabricband, a cable and/or a net. It is practical for the carrier element tobe flexible. It is particularly easy for the envelope body, arranged ona cable, to be positioned in the water, since one end of the cable isfastened to a further carrier element, net and/or cable having a massbody on the ground, and the other end of the cable is held on thesurface of the water by a floating body. The envelope bodies can thus bepositioned without difficulty, particularly in the vertical direction.

It is particularly advantageous that the envelope body is a part of thecarrier element and/or the envelope bodies and the carrier body areproduced as a single piece from the same material. It is therebypossible to produce a single-piece carrier element having integrated gasvolumes, in which the carrier element then constitutes the envelopebody.

The device is optimized in that the carrier element and the envelopebody are produced as a single piece from a thin, elastic tube material,the envelope bodies of like and/or differing sizes being delimited byconstrictions or weld webs of the tube material. Such a carrier elementis particularly easy to produce. For example, in this case it ispossible for the carrier element to be realized as a plastic tube, whosecontinuity is interrupted at certain intervals by constrictions or weldwebs, the resultant space between the constrictions or weld websoptionally being finable with a pressurized gas or remaining empty.

For a time-limited application, for example in the case of constructionwork, it is advantageous that the envelope body and/or the carrierelement is/are produced from a biologically degradable material. Sincesuch materials decompose without residue, they can remain in the waterafter the end of the sound emission, without affecting flora and fauna.The use of such expendable products is also economically efficient,since no recovery costs are incurred.

It is advantageous that the envelope bodies are provided with thecarrier element for the purpose of fastening to the sound source. Sincethe gas volumes enclosed by the envelope body are put into the watertogether with the driven pile, it is possible, partly or entirely, todispense with separate placing of gas bubbles, thereby reducing thecosts of setting up the construction site. The envelope bodies fasteneddirectly to the driven pile disintegrate when they reach the ground,whereby the gas volume is released, rises up as a natural gas bubble andis lost. The empty envelope body and the carrier element then remain onthe ground and decompose over time. The envelope bodies in this case canbe fastened, with the carrier element, to the sound source either singlyor in a plurality of layers.

It is advantageous that the device is arranged in the water-filledinterior of a component and/or of a driven pile realized, in particular,as a steel tube. This enables the device to be arranged in the componenteven before the latter is shipped. There is then no manipulation of thedevice according to the invention at the construction site, thissignificantly improving the application and, in particular, thecost-effectiveness of the device.

It proves to be particularly expedient that the carrier element isarranged in a cage. Such a cage can be prepared industrially on land,for the specific intended application, and is then erected at theapplication site. This provides for the realization of bubble curtainsof any given concentration of bubbles, as well as greater dimensions ofthe width, length, height and diameter of the device.

For optimal exploitation of this property, it is appropriate that thecage, in its supporting structure, is composed of a solid material suchas metal or plastic and/or that a plurality of cages can be arrangedand/or fixed above and next to one another. It is thus possible for thecages to be made from ISO containers without wall faces, this enablingthe cages to be transported without difficulty on land and to water, andbeing extremely cost-effective.

It is extremely useful that the envelope bodies can be fixed in a cageby means of the carrier elements. Thus, it is possible for the envelopebodies to be prepared industrially on land for the specific intendedapplication. The envelope bodies can be filled with gas on land and/orsubsequently in the water. In the cage, the gas-filled envelope bodiesare protected in a simple manner against excessive mechanical load, andcan be transported on land and on water without difficulty. In addition,the setting-up and recovery of the envelope bodies at the applicationsite can thus be effected rapidly, and with standardized equipment.After use, the cages are simply recovered from the water and can bereused.

Another advantageous exploitation of the invention consists in that atleast two cages can be arranged telescopically within one another. Thisprovides for compact transport on land and for rapid set-up anddismantling in the water.

It is advantageous that the envelope body has a valve. By means of thevalve, it is possible for the gas pressure in the envelope body to bealtered before, during and/or after an application. It is particularlyadvantageous in this case that the valves of a plurality of envelopebodies are connected to one another. This enables the gas pressure to bealtered simultaneously in a plurality of envelope bodies.

It is advantageous that each individual envelope body can be filledindividually with a different gas and/or at a different pressure. Thus,it is possible for each envelope body to be produced with the requiredresonance and damping properties, according to the requirements, such asposition, water depth and sound frequency.

It is particularly practical that the device is provided with a floatingbody. The floating body, which is always on the surface of the water,enables the device to be transported, laid out and retrieved in a simplemanner, for example in a manner similar to that of a fishing net.

It proves expedient that the device can be deployed invisibly underwater in coastal protection, for example off the coast, as a wavebreaker in harbor entrances, in order to reduce the waves. If two groupsof envelope bodies, for example in cages, are set up so as to standparallel to one another in the water, an effect is achieved whereby thewave motions between the groups are reduced, in a manner similar to thatof a splitter attenuator. With such an arrangement it is possible, forexample, to reduce the wave motions in relatively open or unprotectedharbors.

It is advantageous that individual envelope bodies and/or carrierelements can be filled on-site with a gas, for example compressed air,for the purpose of supplementing existing envelope bodies and/orgenerating buoyancy, stability and/or for the purpose of spatialdevelopment of the device. This enables the device to be transported asa compact pack to the application site and, for example, the spatialdevelopment of the device under water to be realized by means ofcompressed air, without the deployment of personnel, or with deploymentof only a small number of personnel.

It is advantageous that the device can be used for shielding hydrosoundand waves. This makes it possible, for example, for seismicinvestigations of a bed of a body of water to be shielded againstexternal interference noises.

It has proved expedient that individual envelope bodies or a pluralityof envelope bodies are arranged in a protective housing, in particularmade of a wire mesh or of a dimensionally stable plastic, the protectivehousing having at least one opening, and the water being able to flowthrough the protective housing. This enables the sensitive envelopebodies, for example made from thin latex, to be protected againstdamage. The envelope bodies are subjected to high mechanical loads,particularly during transport and installation, but can also be damagedin the water by animals, for example by being eaten, or by objectstransported by the current.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention permits various embodiments. To elucidate the basicprinciple of the invention, two embodiments thereof are represented inthe drawing and described in the following. In the drawing:

FIG. 1 shows a schematic side view of a device;

FIG. 2 shows a cut and enlarged representation of a portion of thedevice shown in FIG. 1;

FIG. 3 shows a horizontally cut schematic representation of an offshoreconstruction site with the device according to the invention;

FIG. 4 shows a schematic representation of a section through an offshoreconstruction site with the device according to the invention, in a firstembodiment;

FIG. 5 shows a schematic representation of a section through an offshoreconstruction site with the device according to the invention, in asecond embodiment.

DETAILED DESCRIPTION

FIGS. 1 and 2 show a device 3 having a carrier element 2. In theembodiment represented here, the carrier element 2 is composed of amultiplicity of tubes made of a plastic film. Each individual tube isdivided into a plurality of portions. Individual portions are filledwith a gas and constitute pressurized envelope bodies 1 that are at adistance from one another. The individual portions are divided by weldwebs 4. The portions differ in size. In the embodiment shown here,portions that are not filled with a gas have a perforation 5.

FIG. 3 shows a schematic representation of an offshore constructionsite, cut horizontally in the plane E-E of FIG. 4, in which a drivenpile 6 is driven into the ground. The device 3 has a multiplicity ofgas-filled envelope bodies 1, which are at a distance from one another,flexibly connected to one another, and are each surrounded by water 8 onall sides. This enables water 8 to flow through the device 3, inparticular in the direction of sound propagation. Thus, water currentsand animals can pass the device 3 without exerting large forces upon thedevice 3. The envelope bodies 1 in this case are arranged at a distanceradially, axially and in the circumferential direction from the body 6emitting the hydrosound.

FIG. 4 shows a schematic representation of a section through an offshoreconstruction site, in which a driven pile 6 is driven into the ground 7.The device 3 is arranged so as to surround the driven pile 6 in thewater 8. The device 3 is composed of a net 9, on which carrier elements2 are arranged. Envelope bodies 1 that enclose gas are fastened to thecarrier elements 2. The envelope bodies 1 in this case are arranged at adistance radially, axially and in the circumferential direction from thebody 6 emitting the hydrosound. In order to counter the buoyancy of thegas, the net 9 is fixed to the ground by means of mass bodies 10. Abovethe surface of the water, the net 9 is fastened to floating bodies 11.

FIG. 5, like FIG. 4, shows a section through an offshore constructionsite, in which a driven pile 6 is driven into the ground 7. In contrastto FIG. 3, the device 3 surrounding the driven pile 6 in the water 8 iscomposed of cages 12. The cages 12 are open, and water 8 flows throughthem, as in the case of the net 9 in FIG. 4. The envelope bodies 1enclosing the gas are fastened in the cages 12 by means of the carrierelements 2 clamped in the cages 12. A plurality of cages 12 can bestacked next to and above one another. Likewise, it is possible torealize the cages 12 in such a way that a plurality of cages 12 fit intoone another and are drawn apart telescopically at the application site.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Itwill be understood that changes and modifications may be made by thoseof ordinary skill within the scope of the following claims. Inparticular, the present invention covers further embodiments with anycombination of features from different embodiments described above andbelow.

The terms used in the claims should be construed to have the broadestreasonable interpretation consistent with the foregoing description. Forexample, the use of the article “a” or “the” in introducing an elementshould not be interpreted as being exclusive of a plurality of elements.Likewise, the recitation of “or” should be interpreted as beinginclusive, such that the recitation of “A or B” is not exclusive of “Aand B,” unless it is clear from the context or the foregoing descriptionthat only one of A and B is intended. Further, the recitation of “atleast one of A, B and C” should be interpreted as one or more of a groupof elements consisting of A, B and C, and should not be interpreted asrequiring at least one of each of the listed elements A, B and C,regardless of whether A, B and C are related as categories or otherwise.Moreover, the recitation of “A, B and/or C” or “at least one of A, B orC” should be interpreted as including any singular entity from thelisted elements, e.g., A, any subset from the listed elements, e.g., Aand B, or the entire list of elements A, B and C.

What is claimed is:
 1. A device for damping hydrosound in liquid havinga frequency range emitted from a sound-emitting body in the liquid, thedevice comprising: a plurality of envelope bodies distributed in theliquid in an area of the hydrosound-emitting body and at a distance fromeach other, wherein each of the bodies includes a thin-walled, elasticmaterial enclosing a gas and wherein a natural frequency of the envelopebody corresponds to the frequency range of the hydrosound so as todampen the hydrosound; at least one mass body disposed in the liquid,the envelope bodies being connected to the at least one mass body so asto prevent the envelope bodies from rising up in the liquid.
 2. Thedevice as recited in claim 1, wherein the frequency range is from 100 Hzto 1000 Hz.
 3. The device as recited in claim 2, wherein each of theplurality of envelope bodies has a diameter in a range from millimetersto a few centimeters.
 4. The device as recited in claim 1, wherein thefrequency range is from 50 Hz to 600 Hz.
 5. The device as recited inclaim 1, wherein the frequency range is above 1000 Hz.
 6. The device asrecited in claim 5, wherein each of the plurality of envelope bodies hasa diameter in a range of a few millimeters and below.
 7. The device asrecited in claim 1, wherein the plurality of envelope bodies aredistributed radially about the hydrosound-emitting body.
 8. The deviceas recited in claim 1, wherein the plurality of envelope bodies aredistributed so as to form a shield.
 9. The device as recited in claim 1,wherein the plurality of envelope bodies are positioned vertically orhorizontally relative to one another in at least one plane.
 10. Thedevice as recited in claim 1, wherein each of the plurality of envelopebodies is fastened to the hydrosound-emitting body.
 11. The device asrecited in claim 1, wherein at least one of the plurality of envelopebodies and a carrier element connecting at least a portion of theenvelope bodies is composed of at least one of an organic, inorganic anda biologically degradable material.
 12. The device as recited in claim1, further comprising at least one carrier element connecting at leastone of the plurality of envelope bodies to the mass body, each carrierelement being formed as a single piece with at least one of theplurality of envelope bodies from a thin, elastic tube material, andwherein the at least one of the plurality of envelope bodies isdelimited by constrictions or weld webs of the tube material.
 13. Thedevice as recited in claim 1, wherein the mass body includes at leastone cage, and wherein at least one of the plurality of envelope bodiesis disposed in the cage.
 14. The device as recited in claim 13, whereinthe at least one cage includes at least two cages telescopicallydisposable within one another.
 15. The device as recited in claim 1,wherein each of the plurality of envelope bodies includes a valve. 16.The device as recited in claim 1, wherein each of the plurality ofenvelope bodies is configured to be filled with at least one of adifferent gas or a different pressure.
 17. The device as recited inclaim 1, further comprising a floating body connected to at least aportion of the envelope bodies.
 18. The device as recited in claim 1,wherein the envelope bodies are connected to a net.
 19. The device asrecited in claim 1, wherein the device is configured to permit water toflow therethrough in a direction of propagation of the hydrosound.
 20. Adevice for damping hydrosound in liquid having a frequency range emittedfrom a sound-emitting body in the liquid, the device comprising: aplurality of envelope bodies distributed in the liquid at a distancefrom each other, wherein each of the bodies includes a thin-walled,elastic material enclosing a gas and wherein a natural frequency of theenvelope body corresponds to the frequency range of the hydrosound so asto dampen the hydrosound.
 21. The device as recited in claim 20, whereinthe frequency range is from 100 Hz to 1000 Hz.
 22. The device as recitedin claim 21, wherein each of the plurality of envelope bodies has adiameter in a range from millimeters to a few centimeters.
 23. Thedevice as recited in claim 20, wherein the plurality of envelope bodiesare distributed radially about the hydrosound-emitting body.
 24. Thedevice as recited in claim 20, wherein the plurality of envelope bodiesare distributed so as to form a shield.
 25. The device as recited inclaim 20, wherein a group of the envelope bodies are connected to oneanother by a carrier element.
 26. The device as recited in claim 25,wherein the carrier element is attached to a mass body so as to hold thegroup of envelope bodies
 27. A device for damping hydrosound in liquidhaving a frequency range emitted from a sound-emitting body in theliquid, the device comprising: a plurality of envelope bodiesdistributed in the liquid in an area of the hydrosound-emitting body andat a distance from each other, wherein a natural frequency of theenvelope body corresponds to the emitted frequency range of thehydrosound so as to dampen the hydrosound, at least a portion of theenvelope bodies including a foam-like open pore or closed pore material;and at least one mass body disposed in the liquid, the envelope bodiesbeing connected to the at least one mass body so as to prevent theenvelope bodies from rising up in the liquid.
 28. The device as recitedin claim 27, wherein the plurality of envelope bodies are distributedradially about the hydrosound-emitting body.
 29. The device as recitedin claim 27, wherein the plurality of envelope bodies are distributed soas to form a shield.
 30. The device as recited in claim 27, wherein theplurality of envelope bodies are positioned vertically or horizontallyrelative to one another in at least one plane.
 31. The device as recitedin claim 27, wherein each of the plurality of envelope bodies isfastened to the hydrosound-emitting body.
 32. The device as recited inclaim 27, further comprising at least one carrier element connecting atleast one of the plurality of envelope bodies to the mass body.
 33. Thedevice as recited in claim 27, wherein the mass body includes at leastone cage, and wherein at least one of the plurality of envelope bodiesis disposed in the cage.
 34. The device as recited in claim 33, whereinthe at least one cage includes at least two cages telescopicallydisposable within one another.
 35. The device as recited in claim 27,wherein each of the plurality of envelope bodies is configured to befilled with at least one of a different gas or a different pressure. 36.The device as recited in claim 27, further comprising a floating bodyconnected to at least a portion of the envelope bodies.
 37. The deviceas recited in claim 27, wherein the envelope bodies are connected to anet.
 38. The device as recited in claim 27, wherein the device isconfigured to permit water to flow therethrough in a direction ofpropagation of the hydrosound.